NIST provides an exposure facility for high neutron fluencies called the Californium Neutron irradiation Facility (CNIF).
A high-activity Cf-252 source is housed in a large (approximately 15 m x 10 m x 10 m high) room with concrete walls, floor, and ceiling (see photograph). In addition, there are two monoenergetic neutron generators for 2.5 MeV and 14 MeV neutrons. Inside the concrete is a 5.4 cm thick shell (5.3 m x 5.3 m x 5.9 m high) of anhydrous borax. The anhydrous borax prevents neutrons scattered by the concrete from returning to the source. Typical irradiations include sample activation experiments, electronic damage studies, and other special tests requiring high neutron fluence and a low-room-scatter environment. The two most recent irradiation were performed for the Georgetown University Medical Center and Sandia National Laboratory. Interference between successive calibrations through sulfur activation has been identified and eliminated by appropriate scheduling. NIST provides reference high-intensity Cf-252 neutron exposures in support of US nuclear programs.